Hitherto, for example, various airbag apparatuses for restraining a body of an occupant in collision of an automobile or the like, such as an airbag apparatus for use in a driver's seat, which is expanded and deployed from a rotation center of a steering wheel in a driver's seat to a driver side, an airbag for use in a passenger seat, which is expanded and deployed from an instrument panel to a passenger seat side, or the like are used.
Recently, in a case that a large scale accident, in which a large external force is applied to the automobile, such as an overturn of a vehicle body due to a collision or the like, falling of a heavy load such as a fallen tree, or the like occurs, there is a possibility in which an impact is applied to a head from above a head of the occupant by an impact occurred at that time, therefore an airbag apparatus corresponding to such a case is already proposed (for example, refer to Japanese Unexamined Patent Application Publication No. 2002-37011).
In the aforementioned hitherto known technology, a basic configuration, in which an airbag constructed of a bag-shaped body where a base cloth is combined is housed in a backrest portion (or a headrest) of a seat of a vehicle, and a pressurized fluid from an inflator is supplied to the airbag in an emergency and expands the airbag, and which the airbag is deployed above the head of the occupant, is disclosed.
In order to intend an optimization for the airbag apparatus, a further smooth deploying capability of the airbag is required.